1. Field of the Invention
This invention relates to a digital recording and reproducing apparatus which is capable of recording and reproducing recorded data by using a removable external memory as a recording medium.
2. Description of the Related Art
As a digital recording and reproducing apparatus of the above-mentioned kind, a sound recording and reproducing apparatus is known which uses a card-type removable memory (hereinafter referred to as the xe2x80x9cmemory cardxe2x80x9d) as a recording medium. In this sound recording and reproducing apparatus, an analog sound signal input via a microphone is subjected to analog-to-digital conversion to generate sound data, and the sound data is recorded in the memory card. In this case, in a sound recording and reproducing apparatus of this kind, generally, when production of sound data in a memory card has been completed, FAT (File Allocation Table) data of the sound data is recorded in a FAT data recording area of the memory card. On the other hand, when a sound is to be reproduced, sound data thereof is read out from the memory card in accordance with the FAT data, and then digital-to-analog conversion of the sound data is carried out to thereby generate an analog sound signal. This analog sound signal is sounded from a speaker or an earphone.
The above sound recording and reproducing apparatus, however, suffers from the following problems: In the sound recording and reproducing apparatus, a general-purpose memory card is employed as a recording medium for recording sound data. In this case, the memory card is configured such that it can be removed from the sound recording and reproducing apparatus and used in another sound recording and reproducing apparatus or a personal computer, and moreover such that it can reproduce a sound based on sound data and edit the sound data by using the apparatus or the personal computer. This makes it possible to dishonestly rewrite sound data recorded in the memory card. On the other hand, differently from analog sound data recorded by an analog recording and reproducing apparatus, digital sound data recorded by the digital recording and reproducing apparatus makes it difficult, for instance, even if part of the sound data was overwritten, to clearly recognize a boundary between original sound data originally recorded in the memory card and the overwritten sound data. Therefore, it is difficult for the conventional sound recording and reproducing apparatus to determine whether or not the present sound data is overwritten, and further whether or not the sound data is authentic.
In the above case, if part of sound data was overwritten in a quite normal fashion, FAT (File Allocation Table) data of the sound data is replaced by FAT data of new sound data, so that there is generated FAT data which is different from an original FAT data in date information and recording address information. Therefore, when sound data was recorded in the memory card, if FAT data of the sound data is caused to be stored in a built-in memory, and it is determined, when a sound is reproduced based on the sound data, whether or not FAT data items stored in the memory card and the built-in memory respectively are identical to each other, it is possible to determine whether or not the sound data was rewritten. However, since FAT data itself can be rewritten relatively easily, it is possible, for instance, to rewrite the sound data dishonestly to restore FAT data having the same contents with those of FAT data corresponding to the original sound data. This makes it difficult, when the FAT data was restored, to determine whether or not the sound data was rewritten in spite of the fact that the sound data was rewritten.
Further, to prevent sound data from being rewritten by a third party, there have been already devised a technique which records a predetermined user identification code in a memory card in advance such that only a sound recording and reproducing apparatus which first recorded sound data in the memory card can rewrite the sound data, and a technique which encrypts sound data per se to thereby disable rewriting of the sound data by another sound recording and reproducing apparatus. According to the former technique, rewriting of recording data can be prevented. However, it is required to record beforehand user identification codes different from each other in a manner associated with a corresponding one of a very large number of memory cards since it is necessitated to record a user identification code in each memory card in advance. Consequently, the user identification codes themselves become complicated and large-sized codes. Therefore, an important data recordable area of the memory card is occupied by the large-sized codes. Further, it takes a long time period to carry out identification processing for identification of a complicated and large-sized user identification code, and at the same time necessitates a sophisticated identification program and a high performance control section, which results in increased manufacturing costs of the sound recording and reproducing apparatus. On the other hand, the latter technique which encrypts sound data per se suffers from the problem that it takes a longer time period to carry out recording processing for recording sound data due to intricate encryption processing, and moreover it takes a longer time period to carry out reproduction processing for reproducing sound data due to decoding processing for decoding the encrypted sound data. Additionally, a sophisticated processing program for encrypting and decoding sound data and a high performance control section are necessitated.
It is a main object of the invention to provide a digital recording and reproducing apparatus which is capable of determining whether or not recording data was rewritten, reliably and in a short time period without increasing manufacturing costs thereof.
To attain the above object, the invention provides a digital recording and reproducing apparatus which is capable of having a removable external memory mounted therein, for performing recording of recording data in the external memory and reproduction based on the recording data recorded in the external memory, the digital recording and reproducing apparatus comprising an identification data-generating block for generating identification data for use in determining whether or not the recording data was rewritten, an internal memory in which the identification data can be recorded, and a control block for recording the identification data in the external memory as part of the recording data and at the same time recording the identification data in the internal memory in a manner correlated to a title of a file to be recorded in FAT data concerning the recording data, wherein when the control block reads in the recording data from the external memory, if the identification data corresponding to the title of the file in the FAT data concerning the recording data read in from the external memory exists in the internal memory, the control block compares the existing identification data and the identification data recorded in the recording data read in with each other, and carries out predetermined processing if the compared identification data are different from each other.
The digital recording and reproducing apparatus according to the invention includes the identification data-generating block for generating identification data, the internal memory in which the identification data can be recorded, and the control block for recording the identification data recorded in the external memory in the internal memory in a manner correlated to the title of the file of the recording data, and when the identification data corresponding to the title of the file of the recording data exists in the internal memory, the control block compares the two identification data recorded in the external memory and the internal memory, respectively, and carries out predetermined processing if the identification data are different from each other. This makes it possible to determine whether or not the recording data was rewritten, reliably and in a short time period although the apparatus is simple in construction, whereby it is possible to carry out suitable reproduction processing and notification processing for notifying the operator that the recording data has been rewritten, based on results of the determination. Further, differently from the method of fixedly recording an identification code beforehand in an external memory, it is possible to reduce the manufacturing costs of the external memory itself, and therefore it is possible to use an inexpensive memory available on the market as a recording medium.
In this case, it is preferred that the control block records the identification data in a header information recording portion of the recording data when the recording data is recorded in the external memory.
According to this preferred embodiment, the control block records the identification data in the header information recording portion of the recording data, whereby the identification data can be recorded in the recording data even immediately after the start of a recording process when the amount of the recording data per se is not finally determined. Further, during a reproduction process, it is possible to read out the identification data from the header information recording portion in a short time period to determine identity of the recording data, which makes it possible to shorten time periods required both for the recording process and the reproduction process.
Alternatively, it is preferred that the control block records the identification data in a data main body recording portion of the recording data when the recording data is recorded in the external memory.
According to this preferred embodiment, the control block records the identification data in the data main body recording portion of the recording data, whereby when compared with the method of recording identification data in the header information recording portion, it is difficult to locate the recording address of the identification data, thereby making it possible to prevent the identification data from being restored dishonestly after the recording data was rewritten. As a result, it can be determined reliably based on the above identification data whether or not the recording data was rewritten.
In this case, it is preferred that the identification data-generating block generates a plurality of items of the identification data according to an amount of the recording data, and wherein the control block scatteringly records the plurality of items of the identification data in the data main body recording portion, and at the same time records recording address information of the items of the identification data in the internal memory in a manner correlated to the title of the file of the recording data, and wherein when the recording data is read in from the external memory, the control block extracts the plurality of items of the identification data scatteringly recorded in the data main body recording portion of the recording data, based on the recording address information corresponding to the title of the file of the recording data, and compares each of the items of the identification data recorded in the internal memory in a manner correlated to the title of the file and each of the extracted items of the identification data, with each other.
According to this preferred embodiment, the identification data-generating block generates a plurality of items of the identification data according to the amount of the recording data. The control block scatteringly records the items of the identification data in the external memory such that the items of the identification data are scattered in the data main body recording portion, and records recording address information of the identification data in the internal memory in a manner correlated to the title of the file of the recording data, whereby e.g. when part of the recording data is rewritten, the identification data scatteringly recorded in the data main body recording portion is written over. Therefore, by comparing this identification data with the identification data recorded in the internal memory, it is possible to reliably determine whether or not the identification data was rewritten. Further, when compared with the method of recording a predefined number of items of the identification data, it is difficult to locate a recording address corresponding to an item of the identification data, thereby making it possible to reliably prevent the identification data from being restored dishonestly after the recording data was rewritten. Further, the method of fixedly defining the number of items of the identification data has points to be improved in that when the amount of recording data is small, the recording data is bloated by recording an unnecessarily large number of items of identification data at very short recording intervals in the recording data, whereas when the amount of recording data is large, it becomes difficult to reliably determine whether or not the recording data was partially rewritten since identification data is recorded at very large recording intervals in the recording data. In contrast, according to the digital recording and reproducing apparatus of the invention, the number of items of the identification data to be recorded is defined depending on the amount of recording data, whereby the recording data can be prevented from being bloated and at the same time it is possible to reliably determine whether or not the recording data was partially rewritten.
Further, it is preferred that the control block defines recording intervals of the plurality of items of the identification data in a random fashion and scatteringly records the plurality of items of the identification data in the data main body recording portion.
According to this preferred embodiment, the control block scatteringly records the plurality of items of the identification data at recording intervals defined in a random fashion, whereby when compared with a case in which recording intervals for recording identification data are defined in advance, it becomes more difficult to locate the recording address of the identification data, which makes it possible to reliably determine whether or not the identification data was restored dishonestly after the recording data had been rewritten, while reducing the amount of identification data.
Further, it is more preferred that when the compared identification data are determined to be different from each other, the control block notifies that the recording data read in from the external memory was rewritten, as the predetermined processing. In this case, it is more preferred that when the items of the identification data are determined to be identical to each other, the reproduction based on the recording data read in from the external memory is permitted without further processing.
According to this preferred embodiment, when the items of the identification data are different from each other, the control block notifies that the recording data was rewritten. As to recording data which was not rewritten, the reproduction process for reproducing the same can be continued without further processing, whereas when the recording data was rewritten, it is possible to notify the operator of the fact e.g. by displaying letters and symbols or delivering alerting sound, thereby stop the reproduction process.
Also, it is preferred that the identification data-generating block generates the identification data such that the identification data contains date information corresponding to a recording date of the recording data.
According to this preferred embodiment, the identification data-generating block the identification data such that the identification data contains date information corresponding to a recording date of the recording data, whereby compared with the method of recording, for instance, fixed numerical value information or the like as identification data, it becomes difficult to locate the recording address of the identification data, so that it is possible to determine more reliably whether or not the recording data was rewritten, although the apparatus is simple in construction.
Further, it is preferred that the identification data-generating block generates the identification data such that the identification data contains numerical value information generated in a random fashion.
According to this preferred embodiment, the identification data-generating block generates the identification data such that the identification data contains numerical value information generated in a random fashion, whereby compared with the method of recording, for instance, fixed numerical value information or the like as identification data, it becomes difficult to locate the recording address of the identification data, so that it is possible to determine more reliably whether or not the recording data was rewritten, and even if the recording data was recorded on the same date, it is possible to determine more reliably whether or not the recording data was rewritten, since it becomes less likely that items of identification data having the same information are generated.
Further, it is preferred that when the present apparatus is applied to a digital recording and reproducing apparatus configured to be capable of recording and reproducing sound data as the recording data, the digital recording and reproducing apparatus includes a sound signal input block for inputting an analog sound signal, a sound data-generating block for generating the sound data by converting the analog sound signal to digital data and compressing the digital data, a sound signal-generating block for decompressing the sound data recorded in the external memory to generate the digital data and converting the digital data to the analog sound signal, and an amplifier circuit for amplifying the converted analog sound signal to output the amplified sound signal.
According to this preferred embodiment, by applying the digital recording and reproducing apparatus according to the present invention to a voice recorder or the like for recording voice data or sound data which can be rewritten relatively easily, such that the apparatus is configured to be capable of recording and reproducing the voice data, it is possible to reliably determine whether or not the voice data was rewritten.
It should be noted that the disclosure of the present specification relates to the subjects included in Japanese Patent Application No. 2000-277535 which was filed with Japanese Patent Office on Sep. 13, 2000, and all of the disclosures thereby are expressly incorporated herein by reference.